1000MPa-grade high-corrosion-resistance locally-formed steel belt and production method thereof

Abstract

The invention discloses a 1000MPa-grade high-corrosion-resistance locally-formed steel belt and a production method. The steel belt comprises the following chemical components in percentage by mass: 0.02 to 0.05 percent of C, less than or equal to 0.20 percent of Si, 0.40 to 0.60 percent of Mn, 0.015 to 0.035 percent of Al, 3.0 to 5.0 percent of Cr, 0.10 to 0.20 percent of Ni, 0.20 to 0.40 percent of Cu, less than or equal to 0.015 percent of S, less than or equal to 0.015 percent of P and the balance of Fe and inevitable impurity elements. The production method comprises the processes of converter smelting, LF refining, RH refining, slab continuous casting, heating, rolling, laminar cooling, coiling and heat treatment after coiling. The yield strength of the steel strip is larger than or equal to 900 MPa, the tensile strength of the steel strip is larger than or equal to 1000 MPa, the elongation of the steel strip is larger than or equal to 10%, the hole expansion rate of the steel strip is larger than or equal to 55%, the steel strip has high corrosion resistance, the corrosion weight loss rate of the steel strip is smaller than 30% compared with Q355B steel, and the steel strip has good local forming performance.

Description

Technical Field

[0001] The invention belongs to the technical field of steel plate production, and in particular relates to a 1000MPa grade high corrosion resistance locally formed steel strip and a production method thereof. Background Art

[0002] Since the transportation industry involves the demand for lightweighting, such as increasing the strength of automobile beams to meet the demand for lightweighting, and increasing the strength of automobile chassis parts from 780MPa to 1000MPa to meet the demand for lightweighting, such as train carriages also involve the use of products with a strength grade of 800MPa or above to achieve lightweighting. Lightweighting of steel products must be achieved through high strengthening. The increase in the strength of steel products will lead to a sharp decrease in their formability, especially cracking during the local forming process, which reduces the service life of parts.

[0003] The advantages and disadvantages of local forming of hot-rolled strip steel are mainly verified by the size of the hole expansion rate. Steels with high hole expansion rates are not prone to cracking during local cold forming. In traditional designs, such steels mainly add silicon, manganese and a certain amount of microalloying elements such as niobium, titanium, and molybdenum according to the requirements of strength. The addition of silicon can effectively reduce the solubility of carbon in austenite, thereby reducing the stability of supercooled austenite and accelerating the occurrence of the phase change process. Secondly, it inhibits the precipitation of carbides during the phase change process, achieves the effect of increasing the ferrite content, and improves the forming performance of such steels. For example, 0.60%-2.0% of silicon is added in CN101641456B to prepare 780MPa high hole expansion steel, and 1.0%-2.0% of silicon is added in CN105506478A to prepare 980MPa high hole expansion steel. However, the addition of higher silicon elements also has an adverse effect on hot rolling and pickling production. The high silicon content makes it difficult to remove the oxide scale on the surface of the strip steel during hot rolling and pickling production, affecting the appearance quality of the product. Molybdenum is often added to high-strength grade products to improve the stability of product performance and reduce the impact of large-sized titanium nitrides on formability. For example, the CN114107794A patent adds more than 0.1% Mo element, but increases the overall manufacturing cost of the product.

[0004] In addition to the demand for lightweight transportation equipment, corrosion resistance is equally important. Currently, most automotive structural parts have poor corrosion resistance and need surface anti-corrosion treatment to increase their service life. How to improve the corrosion resistance of products is also the key to development. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a 1000MPa grade high corrosion-resistant locally formed steel strip and a production method. Through low alloy cost and simplified manufacturing process, the steel has good local forming performance, which can meet the cold processing process production of structural parts of transportation vehicles such as automobiles and trains, and no cracking occurs during the processing.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a 1000MPa grade high corrosion-resistant locally formed steel strip, the chemical composition and mass fraction of the hot-rolled steel strip are: C: 0.02-0.05%, Si≤0.20%, Mn: 0.40-0.60%, Al: 0.015-0.035%, Cr: 3.0-5.0%, Ni: 0.10-0.20%, Cu: 0.20-0.40%, S≤0.015%, P≤0.015%, and the rest are Fe and unavoidable impurity elements.

[0007] Furthermore, the steel strip has a yield strength of ≥900 MPa, a tensile strength of ≥1000 MPa, an elongation of ≥10%, and a hole expansion rate of ≥55%.

[0008] Furthermore, the microstructure of the steel strip is ferrite+bainite+martensite, and the thickness specification is 2.5-4.0 mm.

[0009] Furthermore, the corrosion weight loss rate of the steel strip relative to Q355B steel is less than 30%.

[0010] Another object of the present invention is to provide a method for producing a 1000MPa grade high corrosion-resistant locally formed steel strip, comprising converter smelting, LF refining, RH refining, slab continuous casting, heating, rolling, laminar cooling, coiling, and post-coiling heat treatment process; the heating process adopts a high-temperature fast-firing process, the heating temperature is 1280-1310°C, and the heating time is 120-150min.

[0011] Furthermore, the rolling process of the present invention adopts 3+5 rolling process in rough rolling, including dephosphorization and reducing the surface temperature of the intermediate billet, and adopts low-temperature finishing rolling inlet temperature and high-temperature finishing rolling outlet temperature in the finishing rolling process to increase the rolling speed and improve the surface quality of the strip. The finishing rolling inlet temperature is 950±30℃, and the final rolling temperature is 880±20℃.

[0012] Furthermore, the laminar cooling process uses rear-stage cooling and the coiling temperature is 520±20°C.

[0013] Furthermore, after coiling, heat treatment is performed to homogenize the mechanical properties of the inner and outer rings of the steel coil, release the internal stress of the steel coil, and further precipitate strengthen to improve the strength. The steel coil is placed in a slow cooling pit for aging treatment. The aging temperature is 450-520°C, the aging treatment time is 7-8h, and the cooling rate is ≤5°C / min.

[0014] The inventive principle of the technical solution of the present invention is described as follows: The production process of the cold stamping steel strip for the structural parts of vehicles such as automobiles and trains provided by the present invention comprises the steps of converter smelting, LF refining, RH refining, slab continuous casting, heating, rolling, laminar cooling, coiling, and heat treatment after coiling.

[0015] The design ideas of the chemical composition of the present invention are as follows: C: Carbon is one of the main added elements of this steel grade, which mainly improves the strength of the steel grade. In order to make the strip strength reach more than 1000MPa, the strip microstructure needs a certain martensite content, so the carbon content should not be too low, and its carbon content should be controlled above 0.02%. The strip also needs good formability. If the carbon content is too high, the strength of the martensite formed will be significantly improved, which will affect the local formability and be unfavorable for the cold processing of parts. Therefore, the carbon content shall not exceed 0.05%. In actual production, the carbon content is controlled within the range of 0.02-0.05%.

[0016] Si: Silicon is a common element in structural steel. The addition of silicon seriously affects the surface quality of steel strip, especially high surface quality steel strip products are not easy to add. In the present invention, silicon is not added as an alloy element, but mainly introduced as a residual element when adding other raw materials during the steelmaking process.

[0017] Mn: Manganese element mainly plays the role of solid solution strengthening in the steel of the present invention to improve the strength of the strip steel. The manganese content should not be too high to avoid deterioration of welding performance. The manganese content is controlled at 0.40-0.60%.

[0018] Al: Aluminum is mainly used for deoxidation in the steelmaking process. Secondly, adding a certain amount of aluminum can refine the ferrite grains of the strip steel and improve the strength of the strip steel. In the present invention, the aluminum content is controlled at 0.015-0.035%.

[0019] Ni, Cu: The addition of nickel and copper elements is used to improve the corrosion resistance of the product. Another function of copper is to increase the strength of the strip through precipitation during the aging process after coiling. The Ni content is 0.10-0.20%, and the Cu content is 0.20-0.40%.

[0020] Cr: The main purpose of adding chromium to general steel grades is to improve the corrosion resistance of the product. In this steel grade, on the one hand, it is to improve the corrosion resistance of the product, and on the other hand, it is to form a bainite structure during hot rolling production. With the increase of chromium content, the pearlite transformation moves to high temperature, and the bainite transformation moves to low temperature. After adding chromium to the hot-rolled strip, it can enter the bainite zone and martensite zone at a lower cooling rate during laminar cooling. The traditional production of high local forming steel grades requires rapid cooling after hot rolling to enter the ferrite phase transformation zone. The addition of chromium is more conducive to production stability and can effectively obtain a complex phase structure. When the chromium content increases to more than 3%, the hot-rolled strip structure can effectively form a composite microstructure of bainite and martensite. In the present invention, the chromium content is controlled at 3.0-5.0%.

[0021] The beneficial effects of the above technical solution are: the present invention adopts a high-temperature fast-burning process to heat the ingot, adopts rough rolling multi-point cooling to reduce the intermediate billet entering the finishing rolling temperature, adopts low-temperature finishing rolling inlet temperature and high-temperature finishing rolling outlet temperature to increase the finishing rolling speed and improve the surface quality of the strip. The laminar cooling adopts a rear-stage cooling mode to form a microstructure of ferrite + bainite + martensite, the steel strip has a yield strength of ≥900MPa, a tensile strength of ≥1000MPa, an elongation of ≥10%, and a hole expansion rate of ≥55%, and has good local forming performance and high corrosion resistance. The corrosion weight loss rate of the steel strip relative to Q355B steel is less than 30%, which can meet the requirements of cold processing of structural parts of transportation vehicles such as automobiles and trains. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a typical metallographic structure diagram of the steel according to Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The scheme of the present invention is further described in detail below in conjunction with specific embodiments.

[0024] Examples 1-10 A production method of a high corrosion resistance 1000MPa grade high local forming steel strip, including converter smelting, LF refining, RH refining, slab continuous casting, heating, rolling, laminar cooling, coiling, and post-coiling heat treatment process; the specific process control parameters are as follows: Heating process: the heating temperature range is 1280-1310°C, the heating time is 120-150min, and the heating process parameters of each embodiment are shown in Table 2; Hot rolling process: finishing rolling inlet temperature is 950±30°C, final rolling temperature is 880±20°C, and the rolling process parameters of each embodiment are shown in Table 2; Laminar cooling process: adopt the rear cooling mode; coiling temperature 520±20℃, control parameters of each embodiment are shown in Table 3; Heat treatment after coiling: The steel is rolled into a slow cooling pit for aging treatment, the aging temperature is 450-520°C, the aging treatment time is 7-8h, and the cooling rate is ≤5°C / min. The control parameters of each embodiment are shown in Table 3.

[0025] Attached Figure 1 The typical metallographic structure diagram of the steel of Example 1 of the present invention is shown in the figure. As can be seen from the figure, the metallographic structure of the steel plate of Example 1 includes ferrite, martensite and bainite structures. The figures of the other embodiments are similar and are omitted. The specific chemical composition of the steel strip of Examples 1-10 is shown in Table 1, and the mechanical properties of the steel strip are shown in Table 4. Corrosion resistance comparison The composition of the steel grade Q355B is: C: 0.17%, Si: 0.15%, Mn: 1.1%, Al: 0.025%, S: 0.08%, P: 0.015%, and the rest is Fe and unavoidable impurity elements.

[0026] Table 1 Chemical composition and content of steel strips in various embodiments (%)

[0027] Table 2 Heating and rolling process parameters of Examples 1-10

[0028] Table 3 Laminar cooling and post-coiling heat treatment process parameters for Examples 1-10

[0029] Table 4 Test results of steel strip performance in various examples

[0030] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A 1000MPa grade high corrosion resistance locally formed steel strip, characterized in that: The chemical composition and mass fraction of the hot-rolled steel strip are: C: 0.02-0.05%, Si≤0.20%, Mn: 0.40-0.60%, Al: 0.015-0.035%, Cr: 3.0-5.0%, Ni: 0.10-0.20%, Cu: 0.20-0.40%, S≤0.015%, P≤0.015%, and the rest are Fe and unavoidable impurity elements.

2. A 1000MPa grade high corrosion resistance locally formed steel strip according to claim 1, characterized in that: The steel strip has a yield strength of ≥900MPa, a tensile strength of ≥1000MPa, an elongation of ≥10%, and a hole expansion rate of ≥55%.

3. The 1000MPa grade high corrosion resistance locally formed steel strip according to claim 1, characterized in that: The steel strip has a microstructure of ferrite+bainite+martensite, and a thickness specification of 2.5-4.0 mm.

4. The 1000MPa grade high corrosion resistance locally formed steel strip according to claim 1, characterized in that: The corrosion weight loss rate of the steel strip relative to Q355B steel is less than 30%.

5. A method for producing a 1000MPa grade high corrosion resistant partially formed steel strip according to any one of claims 1 to 4, characterized in that: The production method comprises converter smelting, LF refining, RH refining, slab continuous casting, heating, rolling, laminar cooling, coiling, and heat treatment after coiling; the heating process adopts a high-temperature fast firing process, the heating temperature is 1280-1310°C, and the heating time is 120-150min.

6. The method for producing a 1000MPa grade high corrosion resistant partially formed steel strip according to claim 5, characterized in that: The rolling process adopts 3+5 rolling process in rough rolling, the inlet temperature of finishing rolling is 950±30°C, and the final rolling temperature is 880±20°C.

7. The method for producing a 1000MPa grade high corrosion resistant partially formed steel strip according to claim 5, characterized in that: The laminar cooling process uses rear-stage cooling and the coiling temperature is 520±20°C.

8. A method for producing a 1000MPa grade high corrosion resistant partially formed steel strip according to any one of claims 5 to 7, characterized in that: After coiling, heat treatment is performed, and the steel is rolled into a slow cooling pit for aging treatment. The aging temperature is 450-520° C., the aging treatment time is 7-8 hours, and the cooling rate is ≤5° C. / min.

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